I have developed a kind of visualization for the music extracting bytes from the stream and displaying them in a kind of group of bars moving up and down, pretty cool by the way. Since these bands move like the way the music spectrum would do, I wonder if is there any way of math calculations to get the strength per band or similar, in a way the music gets represented through its frequency, so you can get lowers on the left side and highers on the right.

You can use FFT data for that. FFT data is available from the BASS_ChannelGetData function. Please see the BASS_ChannelGetData documentation for details. Also take a look at the SPECTRUM (or LIVESPEC) example included in the BASS package for a little demonstration.